(Ethylene, vinyl acetal) copolymers and their use in lithographic printing plate precursors

ABSTRACT

An (ethylene, vinyl acetal) copolymer includes (i) a plurality of ethylenic moieties A having a structure according to the formula: 
                         
wherein R 2  and R 3  independently represent hydrogen, a halogen, an optionally substituted linear, branched or cyclic alk(en)yl group, or an optionally substituted aromatic or heteroaromatic group; (ii) a plurality of acetal moieties B having a structure according to the formula:
 
                         
wherein L 1  represents a divalent linking group; X=0 or 1; and R 1  represents an optionally substituted aromatic or heteroaromatic group including at least one hydroxyl group; and (iii) a plurality of acetal moieties C and/or moieties D which are different from the acetal moieties B, and which include at least one nitrogen atom.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2015/060460, filed May 12, 2015. This application claims thebenefit of European Application No. 14168402.7, filed May 15, 2014,which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to (ethylene, vinyl acetal) copolymers andto lithographic printing plate precursors including such copolymers.

2. Description of the Related Art

Lithographic printing typically involves the use of a so-called printingmaster such as a printing plate which is mounted on a cylinder of arotary printing press. The master carries a lithographic image on itssurface and a print is obtained by applying ink to said image and thentransferring the ink from the master onto a receiver material, which istypically paper. In conventional lithographic printing, ink as well asan aqueous fountain solution (also called dampening liquid) are suppliedto the lithographic image which consists of oleophilic (or hydrophobic,i.e. ink-accepting, water-repelling) areas as well as hydrophilic (oroleophobic, i.e. water-accepting, ink-repelling) areas. In so-calleddriographic printing, the lithographic image consists of ink-acceptingand ink-adhesive (ink-repelling) areas and during driographic printing,only ink is supplied to the master.

Lithographic printing masters are generally obtained by the image-wiseexposure and processing of an imaging material called plate precursor.The coating of the precursor is exposed image-wise to heat or light,typically by means of a digitally modulated exposure device such as alaser, which triggers a (physico-)chemical process, such as ablation,polymerization, insolubilization by cross-linking of a polymer or byparticle coagulation of a thermoplastic polymer latex, solubilization bythe destruction of intermolecular interactions or by increasing thepenetrability of a development barrier layer. Although some plateprecursors are capable of producing a lithographic image immediatelyafter exposure, the most popular plate precursors require wet processingsince the exposure produces a difference of solubility or of rate ofdissolution in a developer between the exposed and the non-exposed areasof the coating. In positive working plates, the exposed areas of thecoating dissolve in the developer while the non-exposed areas remainresistant to the developer. In negative working plates, the non-exposedareas of the coating dissolve in the developer while the exposed areasremain resistant to the developer. Most plates contain a hydrophobiccoating on a hydrophilic support, so that the areas which remainresistant to the developer define the ink-accepting, printing areas ofthe plate while the hydrophilic support is revealed by the dissolutionof the coating in the developer at the non-printing areas.

Many lithographic printing plates contain polymeric binders such asphenolic resins which can be baked in order to increase the run lengthon the press. Over the last few years, printing plate materials whichprovide a high run length without baking have become more popularbecause the post-bake oven can be eliminated leading to reduced energyconsumption and less floor space. The trend towards higher printingspeeds on web presses and the use of recycled paper require platecoatings that are characterized by a high abrasion resistance. Unbakedphenolic resins such as novolac, resol or poly(vinyl phenol) have a poorabrasion resistance and cannot provide a high run length in suchconditions.

In the prior art, the run length of lithographic printing plates basedon phenolic resins has been improved by chemical modification of suchbinders. Examples thereof are described in for example WO 99/01795, EP934 822, EP 1 072 432, U.S. Pat. No. 3,929,488, EP 2 102 443, EP 2 102444, EP 2 102 445 and EP 2 102 446. Phenolic resins have also been mixedwith or replaced by other polymers such as poly(vinyl acetal) resins inorder to improve the abrasion resistance of the coating. Suitablepoly(vinyl acetal) resins are described in U.S. Pat. Nos. 5,262,270;5,169,897; 5,534,381; 6,458,511; 6,270,938; WO 2001/9682; EP 1 162 209;U.S. Pat. Nos. 6,596,460; 6,458,503; 6,783,913; 6,596,456; WO2002/73315; WO 2002/96961; WO 2003/79113; WO 2004/20484; EP 1 627 732;WO 2007/17162; WO 2008/103258; WO 2009/5582; U.S. Pat. Nos. 6,255,033;6,818,378; 6,541,181; WO 2009/85093; US 2009/4599; WO 2009/99518; US2006/130689; US 2003/166750; U.S. Pat. No. 5,330,877; US 2005/3296; U.S.Pat. No. 8,084,189; WO 2007/3030; US 2009/0291387; US 2010/0047723 andUS 2011/0059399.

U.S. Pat. No. 8,048,609 discloses a positive-working radiation-sensitiveimageable element including a coating including a water-insolublepoly(vinyl hydroxyaryl carboxylic acid ester) having cyclic imide groupson some of the pendant hydroxyaryl carboxylic acid ester groups whichprovide to the imageable element an improved chemical resistance.

WO 2009/005582 discloses a radiation-sensitive composition including aradiation-absorbing compound, a developability-enhancing composition andan alkaline-soluble polyvinyl acetal resin comprising two differentacetal groups, a first group having an optionally substituted phenol,naphthol or antracenol group and a second group having an optionallysubstituted naphthol group, which exhibits an improved chemicalresistance.

U.S. Pat. No. 5,169,898 discloses a photosensitive composition with animproved solubility in an alkaline developing solution and whichincludes an acid substituted ternary acetal polymer in combination witha diazo resin.

U.S. Pat. No. 7,544,462 discloses a radiation sensitive compositioncomprising an alkali-soluble polymer including a phenolic resin or apolyvinyl acetal resin and a basic N-containing developability-enhancingcomposition, which exhibits an improved presslife even in the presenceof aggressive press chemicals. WO 2004/081662 describes the use ofvarious polyvinyl acetal resins in combination withdevelopability-enhancing compounds in positive-working compositions andelements.

Poly(vinyl acetal) resins are prepared in the art by actualization ofpoly(vinyl alcohol) with aldehydes. Poly(vinyl acetals) used forlithographic printing plate coatings typically comprise both ahydrophobic acetal moiety, which provides the ink-acceptance, and anhydroxyl substituted aromatic acetal moiety, which produces thesolubility differentiation in an alkaline developer upon exposure.

Such poly(vinyl acetal) resins are typically prepared by theactualization of poly(vinyl alcohol) with a mixture of aldehydes, e.g.an aliphatic aldehyde such as butyraldehyde mixed with a phenolicaldehyde such as hydroxybenzaldehyde. The physical and chemicalproperties of such poly(vinyl acetal) resins are highly dependent on thedegree of acetalysation, the ratio of the aliphatic and the aromaticacetal moieties, the stereochemistry and the random or block nature ofthe acetal resin. Small shifts in process conditions during thepreparation of the known acetal resins may produce significantdifferences in the structure of the obtained resin and thus insignificant differences of their properties. For example, incompletedissolution of the poly(vinyl alcohol) reagent may lead to anirreproducible degree of conversion, i.e. a lack of control of thecomposition of the final product. Also the competition and thetransacetylisation which often occurs between the mixed aldehydereagents is difficult to control so that the right balance between thehydrophobicity of the resin and its solubility in an alkaline developercannot always be obtained.

Furthermore, the lithographic properties of the hydrophobic image areasand the hydrophilic non-image areas of a printing plate determine thequality of the prints. The greater the difference between these twoproperties the better the quality of the plate. A measure of thisdifference in properties is the so-called lithographic contrast betweenimage and non-image parts. By applying developing solutions with anenhanced activity—i.e. by applying more aggressive developers—thiscontrast can be improved. However, it is often observed that duringconsecutive development steps, more aggressive development solutionsresult in a higher solid/imaging material loss, a higher loss of fineimage details and/or undercutting (undercutting means that at the edgesof non-exposed areas the underlying part of the layer is partiallyremoved while the upperlying part of the layer is still present,resulting in smaller printing dot areas when the overhanging part of theupperlying part at the edge disappears). In addition, highly alkaline,more aggressive developers containing silicates and/or metasilicates areeffective to remove the imaged portions of the coating, however, theycan react undesirably with aluminum substrates and generate toxic wastesolutions that create problems for disposal. By adding solubilityenhancers to developer solutions, the solubility of the exposed parts inthe developer solution will be enhanced, however, also the non-exposedparts will solubilize more easily. This often results in a lowercontrast and a higher solid loss. In conclusion, there is a need forcoatings having an improved solubility and/or lithographic contrast inless aggressive and more environmentally acceptable developers. At thesame time, the lithographic printing plate should be sufficientlyresistant against application of a variety of treating liquids or inother words, should have a high chemical resistance. Indeed, before,during and after the printing step, a lithographic printing plate is ingeneral treated with various liquids such as for example ink and/orfountain solutions or plate treating liquids for further improving thelithographic properties of the image and non-image areas. Such liquidsare applied for example to improve the hydrophilic properties of thenon-image areas and to protect, restore or even enhance thehydrophobicity of the image areas. It is essential that these fluids donot deteriorate the image and/or the non-image areas throughout and wellafter their application.

In the unpublished patent application PCT/EP2013/075366 filed on Jan. 1,2013, (ethylene, vinyl acetal) copolymers and their use in lithographicprinting plate precursors are disclosed.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide poly(vinylacetal) resins which are suitable for lithographic plate making andwhich have the known advantages of this class of polymers such as a highabrasion resistance but which are intrinsically less susceptible toprocess conditions during their preparation. It is a further object ofthe present invention to provide a positive-working lithographicprinting plate precursor which has a high resistance against platetreating liquids and which provides a printing plate with an excellentlithographic quality after processing in more environmentally acceptabledeveloper solutions.

The lithographic quality of the printing plate is determined by thedifference between the hydrophilicity of the non-image areas and thehydrophobicity of the image areas—herein further referred to as thelithographic contrast. Areas having hydrophilic properties means areashaving a higher affinity for an aqueous solution than for an oleophilicink; areas having hydrophobic properties means areas having a higheraffinity for an oleophilic ink than for an aqueous solution. A highchemical resistance means that the coating is not or substantially notaffected by printing liquids such as ink, e.g. UV-curable ink, fountainsolution, plate and blanket cleaners.

These objects are realized by the (ethylene, vinyl acetal) copolymerdefined below, of which the hydrophobicity is defined by ethylenicmoieties in the backbone of the polymer which can be controlledindependently from the acetal moieties. In the coating of lithographicprinting plates these polymers provide an improved sensitivity andabrasion resistance compared to poly(vinyl acetal) resins of the priorart while the balance between the ink acceptance, arising from theethylenic moieties, and the solubility in a developer, arising from theacetal moieties, can be controlled efficiently. A preferred embodimentof the current invention has the specific feature that the (ethylene,vinyl acetal) copolymer further comprises acetal moieties C and/ormoieties D as described below.

The (ethylene, vinyl acetal) copolymer comprises

-   (i) a plurality of ethylenic moieties A having a structure according    to the following formula:

wherein R² and R³ independently represent hydrogen, a halogen or anoptionally substituted linear, branched or cyclic alk(en)yl group, or anoptionally substituted aromatic or heteroaromatic group; and

-   (ii) a plurality of acetal moieties B having a structure according    to the following formula:

wherein

-   L¹ represents a divalent linking group;-   x=0 or 1; and-   R¹ represents an optionally substituted aromatic or heteroaromatic    group including at least one hydroxyl group; and-   (iii) a plurality of acetal moieties C and/or moieties D which are    different from the acetal moieties B, and which include at least one    nitrogen atom.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention. Specificpreferred embodiments of the invention are also defined below.

DETAILED DESCRIPTION OF THE INVENTION

The poly(vinyl acetal) resin is a copolymer comprising a plurality ofethylenic moieties A, a plurality of acetal moieties B, and a pluralityof acetal moieties C and/or moieties D. Preferably, the poly(vinylacetal) resin comprises a plurality of ethylenic moieties A, a pluralityof acetal moieties B and a plurality of acetal moieties C. The term“ethylenic moiety” is generally understood as the monomeric unit—i.e.the building block making up the polymer—obtained after polymerizationof optionally substituted ethylene. The ethylenic moieties comprise—CH₂—CH₂— as well as mono- and/or di-substituted derivatives thereof.The poly(vinyl acetal) resin of the present invention is further alsoreferred to herein as the “(ethylene, vinyl acetal) copolymer”.

The (ethylene, vinyl acetal) copolymer may be a random or ablock-copolymer. In the latter preferred embodiment, the copolymer mayinclude alternating sequences of blocks consisting of the ethylenicmoieties A, blocks consisting of the acetal moieties B and blocksconsisting of the acetal moieties C and/or moieties D. Such blocks mayrange from small blocks, e.g. comprising less than 5 moieties—i.e. 1, 2,3, 4 or 5 moieties—up to blocks comprising 100 moieties or more.Preferably, the blocks including the ethylenic moieties A, blocksincluding the acetal moieties B and blocks including the acetal moietiesC and/or moieties D independently include about 10 to 90, 15 to 80 or 20to 60 ethylenic moieties. The moieties A may be all the same ordifferent. Likewise, the moieties B, C and/or D may be all the same ordifferent.

The acetal moieties B have a structure according to the followingformula:

wherein

-   L¹ represents a divalent linking group;-   X=0 or 1; and-   R¹ represents an aromatic or heteroaromatic group including at least    one hydroxyl group and optionally one or more additional    substituent(s). The hydroxyl group(s) may be in ortho, meta and/or    para-position on the ring. Preferably, the aromatic or    heteroaromatic group includes one hydroxyl group in meta or para    position on the ring.

Suitable examples of the aromatic group are preferably optionallysubstituted aryl groups such as a phenyl, benzyl, tolyl, ortho- meta- orpara-xylyl group, naphtyl, anthracenyl, phenanthrenyl group and/orcombinations thereof, which may contain, besides the at least onehydroxyl group further optional substituents. The heteroaromatic groupis preferably selected from optionally substituted heteroaryl groupssuch as an optionally substituted furyl, pyridyl, pyrimidyl, pyrazoyl,thiofenyl group and/or combinations thereof, all including at least onehydroxyl group.

In the definition of R¹, the optional substituents on the aromatic orheteroaromatic group may be selected from additional hydroxysubstituents, an alkyl group such as a methyl or ethyl group, an alkoxygroup such as a methoxy or an ethoxy group, an aryloxy group, athioalkyl group, a thioaryl group, —SH, an azo group such as an azoalkylor azoaryl group, an amino, ethenyl, phenyl, alkenyl, alkynyl,cycloalkyl, aryl, heteroaryl or heteroalicyclic group and/orcombinations thereof.

Preferably, R¹ is an optionally substituted phenol or naphthol groupsuch as an optionally substituted 2-,3- or 4-hydroxyphenyl group, a2,3-, 2,4-, 2,5-dihydroxyphenyl, a 1,2,3-trihydroxyphenyl or ahydroxynaphthyl group. More preferably, R¹ is an optionally substitutedphenol group.

The divalent linking group L¹ is preferably selected from an optionallysubstituted alkylene, arylene or heteroarylene, —O—, —CO—, —CO—O—,—O—CO—, —CO—NH—, —NH—CO—, —NH—CO—O—, —O—CO—NH—, —NH—CO—NH—, —NH—CS—NH—,—SO—, —SO₂—, —CH═N—, —NH—NH— and/or combinations thereof. Thesubstituents optionally present on the alkylene, the arylene or theheteroarylene group may be represented by an alkyl group, a hydroxylgroup, an amino group, a (di)alkylamino group, an alkoxy group, aphosponic acid group or a salt thereof. More preferably, the divalentlinking group L¹ represents an optionally substituted alkylene, aryleneor heteroarylene. Most preferably, L¹ represents —CH₂—, —CH₂—CH₂—,—CH₂—CH₂—CH₂— or a phenylene group.

In a highly preferred embodiment, the acetal moieties B have a structureaccording to the following formula:

wherein R¹ is as defined above.

The ethylenic moieties A have a structure according to the followingformula:

wherein R² and R³ independently represent hydrogen, a halogen such aschloro, bromo or iodo group, or an optionally substituted linear,branched or cyclic alk(en)yl group—i.e. an alkyl or alkenyl group—or anoptionally substituted aromatic group or an optionally substitutedheteroaromatic group. Examples of the alkyl group are a methyl, ethyl,n-propyl, n-butyl, n-pentyl, n-hexyl, chloromethyl, trichloromethyl,iso-propyl, iso-butyl, iso-pentyl, neo-pentyl, 1-methylbutyl andiso-hexyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl andmethylcyclohexyl group. Examples of the alkenyl group are ethenyl,n-propenyl, n-butenyl, n-pentenyl, n-hexenyl, iso-propenyl, iso-butenyl,iso-pentenyl, neo-pentenyl, 1-methylbutenyl, iso-hexenyl, cyclopentenyl,cyclohexenyl and methylcyclohexenyl group. The halogen is preferably achloro group. The aromatic group is preferably selected from anoptionally substituted aryl group such as a phenyl, benzyl, tolyl or anortho- meta- or para-xylyl group, an optionally substituted naphtyl,anthracenyl, phenanthrenyl, and/or combinations thereof. Theheteroaromatic group is preferably selected from an optionallysubstituted furyl, pyridyl, pyrimidyl, pyrazoyl or thiofenyl groupand/or combinations thereof. Preferably, R² and R³ independentlyrepresent hydrogen, a chloro group or a methyl group. In a mostpreferred embodiment, R² and R³ represent hydrogen.

In the definition of R² and R³ the optional substituents on the linear,branched or cyclic alk(en)yl group and on the aromatic or heteroaromaticgroup may be selected from an alkoxy group such as a methoxy or anethoxy group, a thioalkyl group, —SH, and/or a combinations thereof. Theoptional substituents on the aromatic or heteroaromatic group mayfurther be selected from an aryloxy group, a thioaryl group, an azogroup such as an azoalkyl or azoaryl group, an amino group and/or acombinations thereof.

In a highly preferred embodiment, the ethylenic moieties A have astructure according to the following formula:

wherein R² is as defined above. Most preferred, R² represents hydrogen.

The (ethylene, vinyl acetal) copolymer comprises besides the moieties Aand B as defined above, a plurality of acetal moieties C and/or moietiesD which are different from the acetal moiety B and which include atleast one nitrogen atom.

The acetal moieties C and/or moieties D preferably have a structureaccording to the following formulae:

wherein

-   L² and L³ represent a linking group;-   y and z independently represent 0 or 1;-   R⁴ and R⁵ independently represent an optionally substituted alkyl    group, or an optionally substituted aromatic or heteroaromatic    group;    with the proviso that in moiety C at least one of R⁴ or L² includes    a nitrogen atom, and in moiety D at least one of R⁵ or L³ includes a    nitrogen atom.

Suitable aromatic or heteroaromatic groups are as defined above for R²or R³. Preferably, R⁴ and R⁵ independently represent an optionallysubstituted phenyl or alkyl group. In the definition of R⁴ and R⁵ theoptional substituents on the alkyl, aromatic or heteroaromatic groupsmay independently represent an alkyl group, a thioalkyl group, a hydroxygroup, a cyano group, a nitro group, an ester, an amide group, —SH, ahalogen such as a chloro, bromo or iodo group, or a group including—CO—NH—, —NH—CO—O—, —NH—CO—NH—, —NH—CS—NH—, —CO—NH—SO₂—, —NH—SO₂—.Preferably, the optional substituents independently represent a groupincluding —CO—NH—, —NH—CO—O—, —NH—CO—NH—, —NH—CS—NH—, —CO—NH—SO₂— or—NH—SO₂—. Most preferably the optional substituents represent —CO—NH₂,—O—CO—NH₂, —SO₂—NH₂, —NH—CO—NH₂ or —NH—CS—NH₂.

In a preferred embodiment R⁴ and R⁵ independently represent an alkyl, anaromatic or heteroaromatic group substituted with a group including—CO—NH—, —NH—CO—O—, —NH—CO—NH—, —NH—CS—NH—, —CO—NH—SO₂— or —NH—SO₂—.

The linking groups L² and L³ preferably independently include anoptionally substituted alkylene such as a methylene, ethylene orpropylene group, an optionally substituted arylene or heteroarylenegroup, —O—, —CO—O—, —CO—NH—, —NH—CO—O—, —NH—CO—S—, —CO—NH—CO—,—NH—CO—NH—, —NH—CS—NH—, —CO—NH—SO₂—, —CO—NR′—, —SO—, —SO₂—, —NR″—SO₂—,—P(═O) (—O—R″′)—O—, —CH═N—, —NH—NH—, —S—, —S—S—, a maleimido groupand/or combinations thereof, wherein R′, R″, R″′ independently representhydrogen or an optionally substituted alkyl, aryl, or heteroaryl group.More preferably, the linking groups L² and L³ independently include analkylene group, —CO—NH—, —NH—CO—O—, —NH—CO—NH—, —NH—CS—NH—, —CO—NH—SO₂—,—NH—SO₂—, and/or combinations thereof. Most preferably, the linkinggroups L² and L³ independently include an alkylene group, —CO—NH—,—CO—NH—SO₂— or —NH—SO₂—, and/or combinations thereof. Alternatively, thelinking groups L² or L³ independently represent an alkylene group.

In a preferred embodiment of the present invention, the acetal moiety Chas a structure according to the following formula:

wherein

-   a=1, 2 or 3; and-   R⁷ represents an alkyl, aromatic or heteroaromatic group including    at least one substituent selected from —CO—NH—, —NH—CO—O—,    —NH—CO—NH—, —CO—NH—SO₂— or —NH—SO₂—. More preferably the at least    one substituent represents —CO—NH₂, —O—CO—NH₂, —CO—NH—SO₂—,    —SO₂—NH₂, —NH—CO—NH₂ or —NH—CS—NH₂. Most preferably the at least one    substituent represents —CO—NH₂, —CO—NH—SO₂— or —SO₂—NH₂.

More preferably, R⁷ in the acetal moiety C represents a (hetero)arylamide, (hetero)aryl sulphonamide or a (hetero)aryl acylsulphonamide.

Most preferably, the acetal moiety C has a structure according to thefollowing formula:

wherein R⁷ represents a (hetero)aryl amide, (hetero)aryl sulphonamide ora (hetero)aryl acylsulphonamide.

In a preferred embodiment, the sum of the amounts of all the moieties A,and of all the moieties B and of all the moieties C and/or moieties D inthe copolymer ranges from 50 to 90 mol %, more preferably from 60 to 80mol %, and most preferably from 65 to 75 mol %. Preferably, the(ethylene, vinyl acetal) copolymer comprises the moieties A, B and C.

The (ethylene, vinyl acetal) copolymer may comprise other monomericunits besides moieties A, B and C and/or D as defined above. Thecopolymer may for example further comprise optionally substituted vinylalcohol, referred to herein as moieties E, and/or moieties F representedby the following formula:

wherein R⁶ represents hydrogen, or an optionally substituted alkylgroup, an optionally substituted aromatic group or an optionallysubstituted heteroaromatic group. Suitable aromatic or heteroaromaticgroups are as defined above for R² to R⁵. In a preferred embodiment, R⁶is an optionally substituted alkyl group, most preferably methyl.

In the above definition of R⁶, the optional substituents alkyl, aromaticor heteroaromatic group may be selected from an alkoxy group such as amethoxy or an ethoxy group, a thioalkyl group, —SH, and/or acombinations thereof. The optional substituents on the aromatic orheteroaromatic group may further be selected from an aryloxy group, athioaryl group, an azo group such as an azoalkyl or azoaryl group, anamino group, and/or a combinations thereof. The amount of vinyl alcoholmoieties E is preferably from 10 to 60 mol %, more preferably from 15 to50 mol %, and most preferably from 20 to 30 mol %. The amount ofmoieties F is preferably between 0 and 10 mol %. Preferably the amountof moieties F is less than 8 mol %, more preferably less than 3 mol %and most preferably less than 1 mol %.

In the present invention, suitable alkyl groups include 1 or more carbonatoms such as for example C₁ to C₂₂-alkyl groups, more preferably C₁ toC₁₂-alkyl groups and most preferably C₁ to C₆-alkyl groups. The alkylgroup may be lineair, cyclic or branched. Suitable lineair or branchedalkyl groups include for example methyl, ethyl, propyl (n-propyl,isopropyl), butyl (n-butyl, isobutyl, t-butyl), pentyl (n-pentyl,isopentyl, neopentyl), 1,1-dimethyl-propyl, 2,2-dimethylpropyl,1-methyl-butyl, 2-methyl-butyl, or hexyl (n-hexyl, iso-hexyl). Suitablecycloalkyl groups are non-aromatic, homocyclic groups containing carbonatoms and may be monocyclic or polycyclic. Examples include cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl or adamantyl.

Preferably the (ethylene, vinyl acetal) copolymer comprises ethylenicmoieties A as defined above in an amount of at least 10 mol %,preferably in a range from 10 to 55 mol %, more preferably in a rangefrom 15 to 45 mol %, and most preferably in a range from 20 to 35 mol %.The acetal moieties B as defined above are preferably present in anamount of at least 15 mol %, preferably in a range from 15 to 60 mol %,more preferably in a range from 20 to 50 mol %, and most preferably in arange from 25 to 45 mol %. The acetal moieties C as defined above, ifpresent, are preferably present in an amount of at least 3 mol %,preferably in a range from 3 to 40 mol %, more preferably in a rangefrom 5 to 35 mol %, and most preferably in a range from 7 to 30 mol %.The acetal moieties D as defined above are, if present, preferablypresent in an amount of at least 3 mol %, preferably in a range from 3to 40 mol %, more preferably in a range from 5 to 35 mol %, and mostpreferably in a range from 7 to 30 mol %. All amounts of the moieties,expressed herein as mol %, refer to the sum of all monomeric units ofthe copolymer.

In a preferred embodiment of the present invention, the (ethylene, vinylacetal) copolymer is represented by the general formula:

wherein R¹, R⁴, R⁶ and L² are as defined above. Preferably R⁶ is anoptionally substituted alkyl group, preferably methyl;

-   m=10 to 55 mol %, more preferably 15 to 45 mol %, and most    preferably 20 to 35 mol %;-   n=15 to 60 mol %, more preferably 20 to 50 mol %, and most    preferably 25 to 45 mol %;-   o=10 to 60 mol %, more preferably 15 to 50 mol %, and most    preferably 20 to 30 mol %;-   p=0 to 10 mol %, more preferably less than 3 mol % and most    preferably less than 1 mol %; and-   q=3 to 40 mol %, more preferably 5 to 35 mol %, and most preferably    7 to 30 mol %.

The numeric average molecular weight (Mn) of the copolymers rangespreferably from 15000 to 250000, more preferably from 25000 to 200000and most preferably from 35000 to 150000. The weight average molecularweight (Mw) of the copolymers ranges preferably from 50000 to 350000,more preferably from 70000 to 325000 and most preferably from 100000 to300000. The numeric average molecular weight (Mn) and the weight averagemolecular weight (Mw) are each determined by size exclusionchromatography.

The copolymer can, besides moieties A to F discussed above, containfurther monomeric units as disclosed in U.S. Pat. No. 5,169,897, WO1993/3068, U.S. Pat. Nos. 5,534,381, 5,698,360, JP 11-212252, JP11-231535, JP 2000-039707, JP 2000-275821, JP 2000-275823, U.S. Pat. No.6,087,066, WO 2001/9682, U.S. Pat. Nos. 6,270,938, 6,596,460, WO2002/73315, WO 2002/96961, U.S. Pat. No. 6,818,378, WO 2004/20484, WO2007/3030, WO 2009/5582 or WO 2009/99518.

The copolymers described herein can be prepared using known reagentiaand reaction conditions including those described in U.S. Pat. Nos.6,541,181, 4,665,124, 4,940,646, 5,169,898, 5,700,619, 5,792,823,5,849,842, WO 93/03068, DE 10011096; DE 3404366, U.S. Ser. No.09/751,660, WO 2001/09682, WO 2003/079113, WO 2004/081662, WO2004/020484, WO 2008/103258, and in JP 09-328,519.

Suitable polymers which can be used as starting material are copolymersof optionally substituted ethylene and vinyl alcohol. Acetalisation oftwo neighbouring vinyl alcohol units thereof with an aldehyde producesacetal moieties B.

Examples of such aldehydes are e.g. phenolic aldehydes such aso-hydroxybenzaldehyde, 4,6-dibromo-2-formylphenol,3,5-dichlorosalicylaldehyde, 2,4-dihydroxybenzaldehyde,3-methoxysalicyladehyde, 6-hydroxysalicylaldehyde,p-chloroglucinaldehyde, m-hydroxybenzaldehyde,3,4-dihydroxy-benzaldehyde, 4-ethoxy-3-hydroxy-benzaldehyde,p-hydroxybenzaldehyde, syringaldehyde,4-hydroxy-3,5-di-tert-butylbenzaldehyde, 6-hydroxy-isophthalaldehydicacid and 1-hydroxy-2-anthraquinonecarboxaldehyde; naphthol aldehydessuch as 2-hydroxy-1-naphthalenealdehyde,4-hydroxy-1-naphthalenecarbaldehyde, 1-hydroxy-2-naphthaldehyde,6-hydroxy-2-naphthaldehyde and1,6,7-trihydroxy-2-naphthalenecarbox-aldehyde; or antracenol aldehydessuch as 1,3-dihydroxy-2-anthracenecarboxaldehyde and2-hydroxy-1-anthracene-carboxaldehyde.

This acetalization reactions generally require addition of a stronginorganic or organic catalyst acid. Examples of catalyst acids arehydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonicacid, alkylsulfonic acid, perfluoroalkylsulfonic acid and otherperfluoro-activated acids. The amount of acid added to the reactionmixture should allow effective protonation of the reagens but should notsignificantly alter the final product by causing unwanted hydrolysis ofthe acetal groups. The applied reaction temperature is preferablybetween 0° C. and the boiling point of the solvent and depends on thekind of reagens and on the desired level of substitution. The reactionproduct obtained often remains in solution even if the initialpoly(ethylene, vinyl alcohol) reagent is not completely dissolved.Organic solvents as well as mixtures of water with organic solvents areused for the reaction. Incomplete dissolution of the poly(ethylene,vinyl alcohol) reagent is a disadvantage that may lead to anirreproducible degree of conversion. Therefore, in order to obtainreproducible products, solvents which allow complete dissolution of theinitial poly(ethylene, vinyl alcohol) reagent in the reaction mixtureare preferred. Suitable organic solvents are alcohols (such as methanol,ethanol, propanol, butanol, and glycol ether), cyclic ethers (such as1,4-dioxane), and dipolar aprotic solvents (such asN,N-dimethylformamid, N-methyl pyrrolidone or dimethyl sulfoxide). Thefinished products may be isolated as a solid, by introducing thereaction mixture into a non-solvent under vigorous stirring, followed byfiltering and drying. Water is especially suitable as a non-solvent forthe polymers. Unwanted hydrolysis of the acetal group containing ahydroxyl-substituted aromatic group takes place much easier than for theacetal groups containing an aliphatic or non-substituted aromatic group.The presence of small amounts of water in the reaction mixture may leadto a decreased degree of acetalization and incomplete conversion of thearomatic hydroxy aldehyde used. In the absence of water, thehydroxy-substituted aromatic aldehydes react with hydroxyl groups ofalcohols immediately and with almost 100% conversion. Therefore, it isdesirable to remove the water from the reaction mixture during thereaction by for example distillation under reduced pressure. Inaddition, the remaining water may be removed by adding organic compoundsto the reaction mixture which form volatile materials and/or inertcompounds upon reaction with water. These organic compounds may bechoosen from e.g. carbonates, orthoesters of carbonic or carboxylicacids such as diethylcarbonate, trimethyl orthoformate, tetraethylcarbonate, and tetraethyl silicate such as silica-containing compounds.The addition of these materials to the reaction mixture typically leadsto 100% conversion of the used aldehydes.

Whithout being limited thereto, specific examples of copolymersaccording to the present invention are given in the following Table:

The (ethylene, vinyl acetal) copolymer can be used as a binder in thecoating of an image recording material such as a lithographic printingplate precursor or a printed circuit board precursor. The lithographicprinting plate precursor preferably includes a heat and/or lightsensitive coating and is preferably positive-working, i.e. afterexposure and development the exposed areas of the coating are removedfrom the support and define hydrophilic (non-printing) areas, whereasthe unexposed coating is not removed from the support and definesoleophilic (printing) areas.

The light and/or heat-sensitive coating which includes the (ethylene,vinyl acetal) copolymer, may comprise one layer or more than one layer.Preferably, the coating comprises at least two layers; a first layer,and a second layer located above said first layer. First layer meansthat the layer is, compared to the second layer, located closer to thelithographic support. The poly(vinyl acetale) binder may be present inthe first layer, in the second layer or in the first and the secondlayer. The poly(vinyl acetal) binder is preferably only present in thesecond layer.

The light and/or heat sensitive coating preferably contains, besides the(ethylene, vinyl acetal) copolymer, an alkaline soluble oleophilicresin. The oleophilic resin present in the coating is preferably apolymer that is soluble in an aqueous developer, more preferably anaqueous alkaline developing solution with a pH between 7.5 and 14. Theoleophilic resin is preferably a phenolic resin selected from a novolac,a resol or a polyvinylphenolic resin. Other preferred polymers arephenolic resins wherein the phenyl group or the hydroxy group of thephenolic monomeric unit are chemically modified with an organicsubstituent as described in EP 894 622, EP 901 902, EP 933 682,WO99/63407, EP 934 822, EP 1 072 432, U.S. Pat. No. 5,641,608, EP 982123, WO99/01795, WO04/035310, WO04/035686, WO04/035645, WO04/035687 orEP 1 506 858. One or more alkaline soluble oleophilic resins may bepresent in the first layer, in the second layer or in both the first andthe second layer. Preferably, one or more alkaline soluble oleophilicresin(s)—preferably a resole resin—is present in the layer including thepoly(vinyl acetal) binder. In the preferred embodiment where thepoly(vinyl acetal) binder is only present in the first layer, one ormore alkaline soluble oleophilic resin(s)—preferably a novolac resin—ispresent in the second layer.

In the preferred embodiment where the poly(vinyl acetal) binder is atleast present in the second layer, the amount of phenolic resinoptionally present in the coating is preferably at least 10% by weightrelative to the total weight of all the components present in thecoating. Preferably, the amount of phenolic resin optionally present inthe coating is between 10 and 40% by weight, more preferably between 12and 35% by weight, most preferably between 15 and 30% by weight.

In the preferred embodiment where the poly(vinyl acetal) binder is onlypresent in the first layer, the amount of phenolic resin present in thecoating is preferably at least 20% by weight, more preferably at least30% by weight and most preferably at least 45% by weight. Alternatively,the amount of phenolic resin in the latter preferred embodiment ispreferably between 25 and 65% by weight, more preferably between 35 and60% wt weight and most preferably between 45 and 55% wt.

The novolac resin or resol resin may be prepared by polycondensation ofaromatic hydrocarbons such as phenol, o-cresol, p-cresol, m-cresol,2,5-xylenol, 3,5-xylenol, resorcinol, pyrogallol, bisphenol, bisphenolA, trisphenol, o-ethylphenol, p-etylphenol, propylphenol, n-butylphenol,t-butylphenol, 1-naphtol and 2-naphtol, with at least one aldehyde orketone selected from aldehydes such as formaldehyde, glyoxal,acetoaldehyde, propionaldehyde, benzaldehyde and furfural and ketonessuch as acetone, methyl ethyl ketone and methyl isobutyl ketone, in thepresence of an acid catalyst. Instead of formaldehyde and acetaldehyde,paraformaldehyde and paraldehyde may, respectively, be used. The weightaverage molecular weight, measured by gel permeation chromatographyusing universal calibration and polystyrene standards, of the novolacresin is preferably from 500 to 150,000 g/mol, more preferably from1,500 to 50,000 g/mol.

The poly(vinylphenol) resin may be a polymer of one or morehydroxy-phenyl containing monomers such as hydroxystyrenes orhydroxy-phenyl (meth)acrylates. Examples of such hydroxystyrenes areo-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene,2-(o-hydroxyphenyl)propylene, 2-(m-hydroxyphenyl)propylene and2-(p-hydroxyphenyl)propylene. Such a hydroxystyrene may have asubstituent such as chloro, bromo, iodo or fluoro group or a C₁₋₄ alkylgroup, on its aromatic ring. An example of such hydroxy-phenyl(meth)acrylate is 2-hydroxy-phenyl methacrylate. The poly(vinylphenol)resin may be prepared by polymerizing one or more hydroxy-phenylcontaining monomer in the presence of a radical initiator or a cationicpolymerization initiator, or by copolymerizing of one or more of thesehydroxy-phenyl containing monomers with other monomeric compounds suchas acrylate monomers, methacrylate monomers, acrylamide monomers,methacrylamide monomers, vinyl monomers, aromatic vinyl monomers ordiene monomers. The weight average molecular weight, measured by gelpermeation chromatography using universal calibration and polystyrenestandards, of the poly(vinylphenol) resin is preferably from 1,000 to200,000 g/mol, more preferably from 1,500 to 50,000 g/mol.

The heat-sensitive coating may further contain one or more otherbinder(s) which is insoluble in water and soluble in an alkalinesolution such as an organic polymer which has acidic groups with a pKaof less than 13 to ensure that the layer is soluble or at leastswellable in aqueous alkaline developers. This additional binder may bepresent in the first layer, in the second layer or in both the first andthe second layer. Preferably, the binder is present in the first layerlocated between the second layer including the poly(vinyl acetale)binder and the hydrophilic support. The binder may be selected from apolyester resin, a polyamide resin, an epoxy resin, an acrylic resin, amethacrylic resin, a styrene based resin, a polyurethane resin or apolyurea resin. The binder may have one or more functional groups. Thefunctional group(s) can be selected from the list of

-   (i) a sulfonamide group such as —NR—SO₂—, —SO₂—NR— or —SO₂—NR′R″    wherein R and R′ independently represent hydrogen or an optionally    substituted hydrocarbon group such as an optionally substituted    alkyl, aryl or heteroaryl group; more details concerning these    polymers can be found in EP 2 159 049;-   (ii) a sulfonamide group including an acid hydrogen atom such as    —SO₂—NH—CO— or —SO₂—NH—SO₂— as for example disclosed in U.S. Pat.    No. 6,573,022; suitable examples of these compounds include for    example N-(p-toluenesulfonyl) methacrylamide and    N-(p-toluenesulfonyl) acrylamide;-   (iii) an urea group such as —NH—CO—NH—, more details concerning    these polymers can be found in WO 01/96119;-   (iv) a star polymer in which at least three polymer chains are    bonded to a core as described in EP 2 497 639;-   (v) a carboxylic acid group;-   (vi) a nitrile group;-   (vii) a sulfonic acid group; and/or-   (viii) a phosphoric acid group.

(Co)polymers including a sulfonamide group are preferred. Sulfonamide(co)polymers are preferably high molecular weight compounds prepared byhomopolymerization of monomers containing at least one sulfonamide groupor by copolymerization of such monomers and other polymerizablemonomers. Preferably, in the preferred embodiment where the poly(vinylacetale) binder is present in the second layer, the copolymer comprisingat least one sulfonamide group is present in the first layer locatedbetween the layer including the poly(vinyl acetale) binder and thehydrophilic support.

Examples of monomers copolymerized with the monomers containing at leastone sulfonamide group include monomers as disclosed in EP 1 262 318, EP1 275 498, EP 909 657, EP 1 120 246, EP 894 622, U.S. Pat. No.5,141,838, EP 1 545 878 and EP 1 400 351. Monomers such as alkyl or aryl(meth)acrylate such as methyl (meth)acrylate, ethyl (meth)acrylate,butyl (meth)acrylate, benzyl (meth)acrylate, 2-phenylethyl(meth)acrylate, hydroxylethyl (meth)acrylate, phenyl (meth)acrylate;(meth)acrylic acid; (meth)acrylamide; a N-alkyl or N-aryl(meth)acrylamide such as N-methyl (meth)acrylamide, N-ethyl(meth)acrylamide, N-phenyl (meth)acrylamide, N-benzyl (meth)acrylamide,N-methylol (meth)acrylamide, N-(4-hydroxyphenyl)(meth)acrylamide,N-(4-methylpyridyl)(meth)acrylate; (meth)acrylonitrile; styrene; asubstituted styrene such as 2-, 3- or 4-hydroxy-styrene, 4-benzoicacid-styrene; a vinylpyridine such as 2-vinylpyridine, 3-vinylpyridine,4-vinylpyridine; a substituted vinylpyridine such as4-methyl-2-vinylpyridine; vinyl acetate, optionally the copolymerizedvinyl acetate monomeric units are at least partially hydrolyzed, formingan alcohol group, and/or at least partially reacted by an aldehydecompound such as formaldehyde or butyraldehyde, forming an acetal orbutyral group; vinyl alcohol; vinyl acetal; vinyl butyral; a vinyl ethersuch as methyl vinyl ether; vinyl amide; a N-alkyl vinyl amide such asN-methyl vinyl amide, caprolactame, vinyl pyrrolydone; maleimide; aN-alkyl or N-aryl maleimide such as N-benzyl maleimide, are preferred.

Suitable examples of sulfonamide (co)polymers and/or their method ofpreparation are disclosed in EP 933 682, EP 982 123, EP 1 072 432, WO99/63407, EP 1 400 351 and EP 2 159 049. A highly preferred example of asulfonamide (co)polymer is described in EP 2 047 988 A in [0044] to[0046].

Specific preferred examples of sulphonamide (co)polymers are polymerscomprising N-(p-aminosulfonylphenyl) (meth)acrylamide,N-(m-aminosulfonylphenyl) (meth)acrylamide N-(o-aminosulfonylphenyl)(meth)acrylamide and or m-aminosulfonylphenyl (meth)acrylate.

(Co)polymers including an imide group are also preferred as a binder inthe heat-sensitive coating. Specific examples include derivatives ofmethyl vinyl ether/maleic anhydride copolymers and derivatives ofstyrene/maleic anhydride copolymers, that contain an N-substitutedcyclic imide monomeric units and/or N-substituted maleimides such as aN-phenylmaleimide monomeric unit and a N-benzyl-maleimide monomericunit. Preferably, this copolymer is present in the first layer locatedbetween the layer including the poly(vinyl acetale) binder and thehydrophilic support. This copolymer is preferably alkali soluble.Suitable examples are described in EP 933 682, EP 894 622 A [0010] to[0033], EP 901 902, EP 0 982 123 A [007] to [0114], EP 1 072 432 A[0024] to [0043] and WO 99/63407 (page 4 line 13 to page 9 line 37).

Polycondensates and polymers having free phenolic hydroxyl groups, asobtained, for example, by reacting phenol, resorcinol, a cresol, axylenol or a trimethylphenol with aldehydes, especially formaldehyde, orketones, may also be added to the heat-sensitive coating. Condensates ofsulfamoyl- or carbamoyl-substituted aromatics and aldehydes or ketonesare also suitable. Polymers of bismethylol-substituted ureas, vinylethers, vinyl alcohols, vinyl acetals or vinylamides and polymers ofphenylacrylates and copolymers of hydroxy-phenylmaleimides are likewisesuitable. Furthermore, polymers having units of vinylaromatics or aryl(meth)acrylates may be mentioned, it being possible for each of theseunits also to have one or more carboxyl groups, phenolic hydroxylgroups, sulfamoyl groups or carbamoyl groups. Specific examples includepolymers having units of 2-hydroxyphenyl (meth)acrylate, of4-hydroxystyrene or of hydroxyphenylmaleimide. The polymers mayadditionally contain units of other monomers which have no acidic units.Such units include vinylaromatics, methyl (meth)acrylate,phenyl(meth)acrylate, benzyl (meth)acrylate, methacrylamide oracrylonitrile.

In a preferred embodiment of the present invention, the coating includesa first layer comprising a binder including a sulfonamide group, animide group, a nitrile group, a urea group, a carboxyl group, a sulfonicacid group and/or a phosphoric acid group, and the copolymer of thepresent invention, and a second layer, located above the first layer,comprising a phenolic resin selected from a novolac, a resol or apolyvinylphenolic resin.

The dissolution behavior of the coating can be fine-tuned by optionalsolubility regulating components. More particularly, developabilityenhancing compounds, development accelerators and development inhibitorscan be used. In the preferred embodiment where the coating comprisesmore than one layer, these ingredients can be added to the first layerand/or to the second layer and/or to an optional other layer of thecoating.

Suitable developability enhancing compounds are (i) compounds which uponheating release gas as disclosed in WO 2003/79113, (ii) the compounds asdisclosed in WO 2004/81662, (iii) the compositions that comprises one ormore basic nitrogen-containing organic compounds as disclosed in WO2008/103258 and (iv) the organic compounds having at least one aminogroup and at least one carboxylic acid group as disclosed in WO2009/85093.

Examples of basic nitrogen-containing organic compounds useful in thedevelopability-enhancing compositions are N-(2-hydroxyethyl)-2-pyrrolidone, 1-(2-hydroxyethyl)piperazine, N-phenyldiethanolamine,triethanolamine,2-[bis(2-hydroxyethyl)amino]-2-hydroxymethyl-1,3-propanediol,N,N,N′,N′-tetrakis(2-hydroxyethyl)-ethylenediamine,N,N,N′,N′-tetrakis(2-hydroxypropyl)-ethylenediamine,3-[(2-hydroxyethyl)phenylamino]propionitrile, andhexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine. PreferablyN,N,N′,N′-tetrakis(2-hydroxypropyl)-ethylenediamine is used. Mixtures oftwo or more of these compounds are also useful. The basicnitrogen-containing organic compounds can be obtained from a number ofcommercial sources including BASF (Germany) and Aldrich Chemical Company(Milwaukee, Wis.).

The basic nitrogen-containing organic compound(s) is preferably presentin the coating in an amount of from 1 to 30% wt, and typically from 3 to15% wt, based on the total solids of the coating composition.

Preferably, one or more of the basic nitrogen-containing organiccompounds are used in combination with one or more acidicdevelopability-enhancing compounds, such as carboxylic acids or cyclicacid anhydrides, sulfonic acids, sulfinic acids, alkylsulfuric acids,phosphonic acids, phosphinic acids, phosphonic acid esters, phenols,sulfonamides, or sulfonimides, since such a combination may permitfurther improved developing latitude and printing durability.Representative examples of the acidic developability-enhancing compoundsare provided in [0030] to [0036] of US 2005/0214677. They may be presentin an amount of from 0.1 to 30% wt based on the total dry weight of thecoating composition. The molar ratio of one or more basicnitrogen-containing organic compounds to one or more acidicdevelopability-enhancing compounds is generally from 0.1:1 to 10:1 andmore typically from 0.5:1 to 2:1.

Development accelerators are compounds which act as dissolutionpromoters because they are capable of increasing the dissolution rate ofthe coating. For example, cyclic acid anhydrides, phenols or organicacids can be used in order to improve the aqueous developability.Examples of the cyclic acid anhydride include phthalic anhydride,tetrahydrophthalic anhydride, hexahydrophthalic anhydride,3,6-endoxy-4-tetrahydro-phthalic anhydride, tetrachlorophthalicanhydride, maleic anhydride, chloromaleic anhydride, alpha-phenylmaleicanhydride, succinic anhydride, and pyromellitic anhydride, as describedin U.S. Pat. No. 4,115,128. Examples of the phenols include bisphenol A,p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone,2,3,4-trihydroxy-benzophenone, 4-hydroxybenzophenone,4,4′,4″-trihydroxy-triphenylmethane, and4,4′,3″,4″-tetrahydroxy-3,5,3′,5′-tetramethyltriphenyl-methane, and thelike. Examples of the organic acids include sulphonic acids, sulfinicacids, alkylsulfuric acids, phosphonic acids, phosphates, and carboxylicacids, as described in, for example, JP-A Nos. 60-88,942 and 2-96,755.Specific examples of these organic acids include p-toluenesulphonicacid, dodecylbenzenesulphonic acid, p-toluenesulfinic acid,ethylsulfuric acid, phenylphosphonic acid, phenylphosphinic acid, phenylphosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipicacid, p-toluic acid, 3,4-dimethoxybenzoic acid, 3,4,5-trimethoxybenzoicacid, 3,4,5-trimethoxycinnamic acid, phthalic acid, terephthalic acid,4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid,n-undecanoic acid, and ascorbic acid. The amount of the cyclic acidanhydride, phenol, or organic acid contained in the coating ispreferably in the range of 0.05 to 20% by weight, relative to thecoating as a whole. Polymeric development accelerators such asphenolic-formaldehyde resins comprising at least 70 mol % meta-cresol asrecurring monomeric units are also suitable development accelerators.

In a preferred embodiment, the coating also contains developerresistance means, also called development inhibitors, i.e. one or moreingredients which are capable of delaying the dissolution of theunexposed areas during processing. The dissolution inhibiting effect ispreferably reversed by heating, so that the dissolution of the exposedareas is not substantially delayed and a large dissolution differentialbetween exposed and unexposed areas can thereby be obtained. Thecompounds described in e.g. EP 823 327 and WO 97/39894 act asdissolution inhibitors due to interaction, e.g. by hydrogen bridgeformation, with the alkali-soluble resin(s) in the coating. Inhibitorsof this type typically are organic compounds which include at least onearomatic group and a hydrogen bonding site such as a nitrogen atom whichmay be part of a heterocyclic ring or an amino substituent, an oniumgroup, a carbonyl, sulfinyl or sulfonyl group. Suitable dissolutioninhibitors of this type have been disclosed in e.g. EP 825 927 and EP823 327. Some of the compounds mentioned below, e.g. infrared dyes, suchas cyanines, and contrast dyes, such as quaternized triarylmethane dyes,can also act as a dissolution inhibitor.

Other suitable inhibitors improve the developer resistance because theydelay the penetration of the aqueous alkaline developer into thecoating. Such compounds can be present in the first layer and/or in theoptional second layer and/or in a development barrier layer on top ofsaid layer, as described in e.g. EP 864 420, EP 950 517, WO 99/21725 andWO 01/45958. The solubility and/or penetrability of the barrier layer inthe developer can be increased by exposure to heat and/or infraredlight.

Water-repellent polymers represent another type of suitable dissolutioninhibitors. Such polymers seem to increase the developer resistance ofthe coating by repelling the aqueous developer from the coating. Thewater-repellent polymers can be added to the first and/or second layerof the coating and/or can be present in a separate layer provided on topof these layers. In the latter preferred embodiment, the water-repellentpolymer forms a barrier layer which shields the coating from thedeveloper and the solubility of the barrier layer in the developer orthe penetrability of the barrier layer by the developer can be increasedby exposure to heat or infrared light, as described in e.g. EP 864 420,EP 950 517 and WO99/21725.

Preferred examples of inhibitors which delay the penetration of theaqueous alkaline developer into the coating include water-repellentpolymers including siloxane and/or perfluoroalkyl units. Thepolysiloxane may be a linear, cyclic or complex cross-linked polymer orcopolymer. The term polysiloxane compound shall include any compoundwhich contains more than one siloxane group —Si(R,R′)—O—, wherein R andR′ are optionally substituted alkyl or aryl groups. Preferred siloxanesare phenylalkylsiloxanes and dialkylsiloxanes. The number of siloxanegroups in the polymer is at least 2, preferably at least 10, morepreferably at least 20. It may be less than 100, preferably less than60.

The water-repellent polymer may be a block-copolymer or agraft-copolymer including a polar block such as a poly- oroligo(alkylene oxide) and a hydrophobic block such as a long chainhydrocarbon group, a polysiloxane and/or a perfluorinated hydrocarbongroup. A typical example of a perfluorinated surfactant is Megafac F-177available from Dainippon Ink & Chemicals, Inc. Other suitable copolymerscomprise about 15 to 25 siloxane units and 50 to 70 alkyleneoxidegroups. Preferred examples include copolymers comprisingphenylmethylsiloxane and/or dimethylsiloxane as well as ethylene oxideand/or propylene oxide, such as Tego Glide 410, Tego Wet 265, TegoProtect 5001 or Silikophen P50/X, all commercially available from TegoChemie, Essen, Germany.

A suitable amount of such a water-repellent polymer in the coating isbetween 0.5 and 25 mg/m², preferably between 0.5 and 15 mg/m² and mostpreferably between 0.5 and 10 mg/m². When the water-repellent polymer isalso ink-repelling, e.g. in the case of polysiloxanes, higher amountsthan 25 mg/m² can result in poor ink-acceptance of the non-exposedareas. An amount lower than 0.5 mg/m² on the other hand may lead to anunsatisfactory development resistance.

It is believed that during coating and drying, the water-repellentpolymer or copolymer acts as a surfactant and tends to position itself,due to its bifunctional structure, at the interface between the coatingand air and thereby forms a separate top layer, even when applied as aningredient of the coating solution. Simultaneously, such surfactantsalso act as spreading agents which improve the coating quality.Alternatively, the water-repellent polymer or copolymer can be appliedin a separate solution, coated on top of the coating including one oroptional more layers. In that preferred embodiment, it may beadvantageous to use a solvent in the separate solution that is notcapable of dissolving the ingredients present in the other layers sothat a highly concentrated water-repellent phase is obtained at the topof the coating.

The coating of the heat-sensitive printing plate precursor preferablyalso contains an infrared light absorbing dye or pigment which, in thepreferred embodiment where the coating comprises more than one layer,may be present in the first layer, and/or in the second layer, and/or inan optional other layer. Preferred IR absorbing dyes are cyanine dyes,merocyanine dyes, indoaniline dyes, oxonol dyes, pyrilium dyes andsquarilium dyes. Examples of suitable IR dyes are described in e.g.EP-As 823327, 978376, 1029667, 1053868, 1093934; WO 97/39894 and00/29214. A preferred compound is the following cyanine dye:

wherein X⁻ is a suitable counter ion such as tosylate.

The concentration of the IR-dye in the coating is preferably between0.25 and 15.0% wt, more preferably between 0.5 and 10.0% wt, mostpreferably between 1.0 and 7.5% wt relative to the coating as a whole.

The coating may further comprise one or more colorant(s) such as dyes orpigments which provide a visible color to the coating and which remainin the coating at the image areas which are not substantially removedduring the processing step. As a result, a visible image is formed whichenables inspection of the lithographic image on the developed printingplate. Such dyes are often called contrast dyes or indicator dyes.Preferably, the dye has a blue color and an absorption maximum in thewavelength range between 600 nm and 750 nm. Typical examples of suchcontrast dyes are the amino-substituted tri- or diarylmethane dyes, e.g.crystal violet, methyl violet, victoria pure blue, flexoblau 630,basonylblau 640, auramine and malachite green. Also the dyes which arediscussed in depth in EP-A 400,706 are suitable contrast dyes. Dyes suchas di- or tri-arylmethane dyes, cyanine dyes, styryl dyes and merostyryldyes, which, combined with specific additives, only slightly color thecoating but which become intensively colored after exposure, asdescribed in for example WO2006/005688 may also be used as colorants.

To protect the surface of the coating of the heat and/or light sensitiveprinting plate precursors, in particular from mechanical damage, aprotective layer may also optionally be applied. The protective layergenerally comprises at least one water-soluble binder, such as polyvinylalcohol, polyvinylpyrrolidone, partially hydrolyzed polyvinyl acetates,gelatin, carbohydrates or hydroxyethylcellulose, and can be produced inany known manner such as from an aqueous solution or dispersion whichmay, if required, contain small amounts—i.e. less than 5% by weightbased on the total weight of the coating solvents for the protectivelayer—of organic solvents. The thickness of the protective layer cansuitably be any amount, advantageously up to 5.0 μm, preferably from 0.1to 3.0 μm, particularly preferably from 0.15 to 1.0 μm.

Optionally, the coating may further contain additional ingredients suchas surfactants, especially perfluoro surfactants, inoragnic fillers orpolymers particles such as matting agents and spacers. Examples ofinorganic fillers include silicon or titanium dioxide particles,zirconium oxide, kaolin clays and derivatives, silicium oxide basedparticles optionally coated and/or modified, alumina oxide, fumed silicaand cerium oxide. The particles can be in the micrometer range,typically between 1 μm and 10 μm. More preferable, the particles are inthe nanometer-range i.e. between 10 nm and 900 nm.

The lithographic printing plate precursor comprises a support which hasa hydrophilic surface or which is provided with a hydrophilic layer. Thesupport may be a sheet-like material such as a plate or it may be acylindrical element such as a sleeve which can be slid around a printcylinder of a printing press. Preferably, the support is a metal supportsuch as aluminum or stainless steel. The support can also be a laminatecomprising an aluminum foil and a plastic layer, e.g. polyester film.

A particularly preferred lithographic support is a grained and anodizedaluminum support. The aluminum support has usually a thickness of about0.1-0.6 mm. However, this thickness can be changed appropriatelydepending on the size of the printing plate used and/or the size of theplate-setters on which the printing plate precursors are exposed. Thealuminium is preferably grained by electrochemical graining, andanodized by means of anodizing techniques employing phosphoric acid or asulphuric acid/phosphoric acid mixture. Methods of both graining andanodization of aluminum are well known in the art.

By graining (or roughening) the aluminum support, both the adhesion ofthe printing image and the wetting characteristics of the non-imageareas are improved. By varying the type and/or concentration of theelectrolyte and the applied voltage in the graining step, different typeof grains can be obtained. The surface roughness is often expressed asarithmetical mean center-line roughness Ra (ISO 4287/1 or DIN 4762) andmay vary between 0.05 and 1.5 μm. The aluminum substrate has preferablyan Ra value between 0.30 μm and 0.60 μm, more preferably between 0.35 μmand 0.55 μm and most preferably between 0.40 μm and 0.50 μm. The lowerlimit of the Ra value is preferably about 0.1 μm. More detailsconcerning the preferred Ra values of the surface of the grained andanodized aluminum support are described in EP 1 356 926.

By anodizing the aluminum support, its abrasion resistance andhydrophilic nature are improved. The microstructure as well as thethickness of the Al₂O₃ layer are determined by the anodizing step, theanodic weight (g/m² Al₂O₃ formed on the aluminium surface) variesbetween 1 and 8 g/m². The anodic weight is preferably between 1.5 g/m²and 5.0 g/m², more preferably 2.5 g/m² and 4.0 g/m² and most preferably2.5 g/m² and 3.5 g/m².

The grained and anodized aluminum support may be subject to a so-calledpost-anodic treatment to improve the hydrophilic character of itssurface. For example, the aluminum support may be silicated by treatingits surface with a solution including one or more alkali metal silicatecompound(s)—such as for example a solution including an alkali metalphosphosilicate, orthosilicate, metasilicate, hydrosilicate,polysilicate or pyrosilicate—at elevated temperature, e.g. 95° C.Alternatively, a phosphate treatment may be applied which involvestreating the aluminum oxide surface with a phosphate solution that mayfurther contain an inorganic fluoride. Further, the aluminum oxidesurface may be rinsed with a citric acid or citrate solution, gluconicacid, or tartaric acid. This treatment may be carried out at roomtemperature or may be carried out at a slightly elevated temperature ofabout 30 to 50° C. A further interesting treatment involves rinsing thealuminum oxide surface with a bicarbonate solution. Still further, thealuminum oxide surface may be treated with polyvinylphosphonic acid,polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinylalcohol, polyvinylsulphonic acid, polyvinylbenzenesulphonic acid,sulphuric acid esters of polyvinyl alcohol, acetals of polyvinylalcohols formed by reaction with a sulphonated aliphatic aldehyde,polyacrylic acid or derivates such as GLASCOL E15™ commerciallyavailable from Ciba Speciality Chemicals. One or more of these posttreatments may be carried out alone or in combination. More detaileddescriptions of these treatments are given in GB-A 1 084 070, DE-A 4 423140, DE-A 4 417 907, EP-A 659 909, EP-A 537 633, DE-A 4 001 466, EP-A292 801, EP-A 291 760 and U.S. Pat. No. 4,458,005.

In a preferred embodiment, the support is first treated with an aqueoussolution including one or more silicate compound(s) as described abovefollowed by the treatment of the support with an aqueous solutionincluding a compound having a carboxylic acid group and/or a phosphonicacid group, or their salts. Particularly preferred silicate compoundsare sodium or potassium orthosilicate and sodium or potassiummetasilicate. Suitable examples of a compound with a carboxylic acidgroup and/or a phosphonic acid group and/or an ester or a salt thereofare polymers such as polyvinylphosphonic acid, polyvinylmethylphosphonicacid, phosphoric acid esters of polyvinyl alcohol, polyacrylic acid,polymethacrylic acid and a copolymer of acrylic acid and vinylphosphonicacid. A solution comprising polyvinylphosphonic acid orpoly(meth)acrylic acid is highly preferred.

The support can also be a flexible support, which may be provided with ahydrophilic layer, hereinafter called ‘base layer’. The flexible supportis e.g. paper, plastic film or aluminum. Preferred examples of plasticfilm are polyethylene terephthalate film, polyethylene naphthalate film,cellulose acetate film, polystyrene film, polycarbonate film, etc. Theplastic film support may be opaque or transparent.

The base layer is preferably a cross-linked hydrophilic layer obtainedfrom a hydrophilic binder cross-linked with a hardening agent such asformaldehyde, glyoxal, polyisocyanate or a hydrolyzedtetra-alkylorthosilicate. The latter is particularly preferred. Thethickness of the hydrophilic base layer may vary in the range of 0.2 to25 μm and is preferably 1 to 10 μm. More details of preferredembodiments of the base layer can be found in e.g. EP 1 025 992.

The lithographic printing plate precursor can be prepared by (i)applying on a support as described above the coating including thepoly(vinyl acetal) resin of the present invention and (ii) drying theprecursor. Any coating method can be used for applying one or morecoating solutions to the hydrophilic surface of the support. Themulti-layer coating can be applied by coating/drying each layerconsecutively or by the simultaneous coating of several coatingsolutions at once. In the drying step, the volatile solvents are removedfrom the coating until the coating is self-supporting and dry to thetouch. However it is not necessary (and may not even be possible) toremove all the solvent in the drying step. Indeed the residual solventcontent may be regarded as an additional composition variable by meansof which the composition may be optimized. Drying is typically carriedout by blowing hot air onto the coating, typically at a temperature ofat least 70° C., suitably 80-150° C. and especially 90-140° C. Alsoinfrared lamps can be used. The drying time may typically be 15-600seconds.

Between coating and drying, or after the drying step, a heat treatmentand subsequent cooling may provide additional benefits, as described inWO99/21715, EP-A 1074386, EP-A 1074889, WO 2000/29214, and WO2004/030923, WO 2004/030924, WO 2004/030925.

According to the present invention there is also provided a method formaking a positive-working lithographic printing plate comprising thesteps of imagewise exposing the printing plate precursor followed bydeveloping the imagewise exposed precursor so that the exposed areas aredissolved in the developer solution.

The heat-sensitive plate precursor can be image-wise exposed directlywith heat, e.g. by means of a thermal head, or indirectly by infraredlight, preferably near infrared light. The infrared light is preferablyconverted into heat by an IR light absorbing compound as discussedabove. The heat-sensitive lithographic printing plate precursor ispreferably not sensitive to visible light, i.e. no substantial effect onthe dissolution rate of the coating in the developer is induced byexposure to visible light. Most preferably, the coating is not sensitiveto ambient daylight, i.e. the wavelength range including near UV light(300-400 nm) and visible light (400-750 nm).

The printing plate precursor can be exposed to infrared light by meansof e.g. LEDs or a laser. Most preferably, the light used for theexposure is a laser emitting near infrared light having a wavelength inthe range from about 750 to about 1500 nm, more preferably 750 to 1100nm, such as a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser. Therequired laser power depends on the sensitivity of the plate precursor,the pixel dwell time of the laser beam, which is determined by the spotdiameter (typical value of modern plate-setters at 1/e² of maximumintensity: 5-25 μm), the scan speed and the resolution of the exposureapparatus (i.e. the number of addressable pixels per unit of lineardistance, often expressed in dots per inch or dpi; typical value:1000-4000 dpi).

Two types of laser-exposure apparatuses are commonly used: internal(ITD) and external drum (XTD) platesetters. ITD plate-setters forthermal plates are typically characterized by a very high scan speed upto 500 m/sec and may require a laser power of several Watts. XTDplatesetters for thermal plates having a typical laser power from about200 mW to about 1 W operate at a lower scan speed, e.g. from 0.1 to 10m/sec. An XTD platesetter equipped with one or more laserdiodes emittingin the wavelength range between 750 and 850 nm is an especiallypreferred embodiment for the method of the present invention.

The known platesetters can be used as an off-press exposure apparatus,which offers the benefit of reduced press down-time. XTD platesetterconfigurations can also be used for on-press exposure, offering thebenefit of immediate registration in a multi-color press. More technicaldetails of on-press exposure apparatuses are described in e.g. U.S. Pat.No. 5,174,205 and U.S. Pat. No. 5,163,368.

After exposure, the precursor is developed whereby the non-image areasof the coating are removed by immersion in a developer, preferably anaqueous alkaline developer, which may be combined with mechanicalrubbing, e.g. by a rotating brush. The developer preferably comprises analkaline agent which may be an inorganic alkaline agent such as analkali metal hydroxide, an organic alkaline agent such as an amine,and/or an alkaline silicate such as an alkali metal silicate or analkali metal metasilicate. Silicate-based developers which have a ratioof silicon dioxide to alkali metal oxide of at least 1 are advantageousbecause they ensure that the alumina layer (if present) of the substrateis not damaged. Preferred alkali metal oxides include Na₂0 and K₂0, andmixtures thereof. A particularly preferred silicate-based developersolution is a developer solution comprising sodium or potassiummetasilicate, i.e. a silicate where the ratio of silicon dioxide toalkali metal oxide is 1. The developer preferably has a pH above 8, morepreferably above 10 and most preferably the developer has a pH between10 and 12. The developer may further contain components such as a buffersubstance, a complexing agent, an antifoaming agent, an organic solvent,a corrosion inhibitor, a dye, an antisludge agent, a dissolutionpreventing agent such as a non-ionic surfactant, an anionic, cationic oramphoteric surfactant and/or a hydrotropic agent as known in the art.The developer may further contain a poly- hydroxyl compound such as e.g.sorbitol, preferably in a concentration of at least 40 g/l, and also apolyethylene oxide containing compound such as e.g. Supronic B25,commercially available from RHODIA, preferably in a concentration of atmost 0.15 g/l. During development, any water-soluble protective layerpresent is also removed. In a preferred embodiment, the developer issubstantially free of silicates e.g. alkali metal silicates or alkalimetal metasilicates. More details concerning the development step can befound in for example EP 2 263 874, WO 2004/071767 and US 2010/0047723.

The development step may be followed by a rinsing step and/or a gummingstep. The gumming step involves post-treatment of the lithographicprinting plate with a gum solution. A gum solution is typically anaqueous liquid which comprises one or more surface protective compoundsthat are capable of protecting the lithographic image of a printingplate against contamination or damaging. Suitable examples of suchcompounds are film-forming hydrophilic polymers or surfactants. Asuitable gum solution which can be used after the development step isdescribed in for example EP 1 342 568 and WO 2005/111727. The plateprecursor can, if required, be further post-treated with a suitablecorrecting agent or preservative as known in the art.

To increase the resistance of the finished printing plate and hence toextend its presslife capability (run length) the layer can be brieflyheated to elevated temperatures (“baking”). The plate can be driedbefore baking or is dried during the baking process itself. During thebaking step, the plate can be heated at a temperature which is higherthan the glass transition temperature of the heat-sensitive coating,e.g. between 100° C. and 230° C. for a period of 40 seconds to 5minutes. Baking can be done in conventional hot air ovens or byirradiation with lamps emitting in the infrared or ultraviolet spectrum.As a result of this baking step, the resistance of the printing plate toplate cleaners, correction agents and UV-curable printing inksincreases. Such a thermal post-treatment is described, inter alia, in DE1,447,963 and GB 1,154,749.

The heat and/or light sensitive printing plates can be used forconventional, so-called wet offset printing, in which ink and an aqueousdampening liquid are supplied to the plate. Another suitable printingmethod uses so-called single-fluid ink without a dampening liquid.Suitable single-fluid inks have been described in U.S. Pat. Nos.4,045,232; 4,981,517 and U.S. Pat. No. 6,140,392. In a most preferredembodiment, the single-fluid ink comprises an ink phase, also called thehydrophobic or oleophilic phase, and a polyol phase as described in WO2000/32705.

EXAMPLES Synthesis of Inventive Resins 2 to 6 and Comparative Resin 1

The structural formulae shown below indicate the monomer composition ofthe prepared resins but the sequence of the moieties is for illustrationonly.

Unless otherwise specified, all compounds and solvents used in theExamples are readily available from fine chemical suppliers such asAcros or Aldrich.

Test Methods

LC-MS Analysis

Method 1

The LC-MS analysis according to method 1 was done on a HP 1100 EsquireLC, using an Altima HP C18 AQ column (150×3, 5 μm), operating at a flowrate of 0.5 ml/min and at 40° C. A gradient elution was used, withwater+0.1% formic acid as eluent A and acetonitrile+0.1% formic acid aseluent B. The gradient according to the following Table was used.

Time % B 0 20 7 100 17 100 17.1 20 20 20

ESI ionisation was used in combination with a combibron detector. 5 μlof a solution of 2 mg of each compound in 10 ml acetonitrile wasinjected.

Method 2

The LC-MS analysis according to method 2 was done on a HP 1100 EsquireLC, using an Altima HP C18 AQ column (150×3, 5 μm), operating at a flowrate of 0.5 ml/min and at 40° C. A gradient elution was used, H₂O/MeOH9/1 containing 10 mmol NH₄OAc as eluent A and MeOH containing 10 mmolNH₄OAc as eluent B. The gradient according to the following Table wasused.

Time % B 0 0 12 100 17 100 18 0 20 0

ESI ionisation was used in combination with a combibron detector. 5 μlof a solution of 2 mg of each compound in 10 ml acetonitrile wasinjected.

¹H-NMR Analysis

A Varian Unity Inova spectrometer was used, using DMSO d6 as solvent at25° C. with DMSO d5 (2.50 ppm) as internal reference at a spectrometerfrequency of 400 MHz.

Synthesis of Comparative Resin 1

13.6 g of an ethylene vinyl alcohol copolymer (27 mol % ethylene, EVALSP521 B, supplied by Kuraray) was dissolved in 50 g dimethyl acetamideat 85° C. 0.3 g (3.13 mmol) methane sulfonic acid in 5.6 g dimethylacetamide was added and the mixture was stirred for 10 minutes at 85° C.12.2 g (0.1 mol) salicylic aldehyde in 11.3 g dimethyl acetamide wasadded slowly while keeping the reaction temperature at 80° C. Thereaction was allowed to continue for 1 hour at 80° C. 11.1 g (0.105 mol)trimethyl orthoformate in 5.6 g dimethyl acetamide was added and thereaction was allowed to continue for 90 minutes at 80° C. 0.92 g (3.13mmol) quadrol (CASRN102-60-3) in 7 g dimethyl acetamide was added andthe reaction mixture was stirred for 10 minutes. The reaction mixturewas allowed diluted with 90 ml 1-methoxy-2-propanol and cooled down toroom temperature. The reaction mixture was further diluted with 100 ml1-methoxy-2-propanol. The mixture was slowly added to 1 1 water toprecipitate comparative resin 1. Comparative resin 1 was isolated byfiltration and treated with a mixture of 400 ml water en 100 ml1-methoxy-2-propanol for 16 hours. Comparative resin 1 was isolated byfiltration and dried. 21 g of comparative resin 1 was isolated.

Comparative resin 1 was analyzed using ¹H-NMR spectroscopy. 20 mg of thepolymer was dissolved in DMSO-d6: the aromatic protons of the polymerbound phenolic fragments: 6.75 ppm (2H), 7.11 ppm (1H), 7.32 ppm (1H),the acetal protons: 5.70 ppm and 5.99 ppm (together 1H), the phenolicproton: 9.30 ppm (1H)).

Synthesis of Inventive Resin 2 Synthesis of hexanoic acid(2,2-dimethoxy-ethyl)amide

105.14 g (1 mol) 2,2-dimethoxy-ethylamine was dissolved in 1000 mltetrahydrofuran. 257.17 g (1.2 mol) hexanoic anhydride, dissolved in 200ml tetrahydrofuran, was added over 30 minutes, while the temperature waskept below 30° C. The reaction mixture was stirred for 10 minutesfollowed by the addition of 121.2 g (1.2 mol) triethyl amine over 5minutes. The reaction was allowed to continue for half an hour at roomtemperature. 500 ml tetrahydrofuran was evaporated under reducedpressure. 300 ml methylene chloride and 450 ml brine were added. Theorganic fraction was isolated. The aqueous fraction was extracted threetimes with 250 ml methylene chloride. The pooled organic fractions weredried over MgSO₄ and evaporated under reduced pressure. Hexanoic acid(2,2-dimethoxy-ethyl)amide was purified using preparative columnchromatography on a GraceResolv RS80 SiOH 35-45 μm (80 g) column, usinga gradient elution from methylene chloride to ethyl acetate. 114 ghexanoic acid (2,2-dimethoxy-ethyl)amide was isolated (y: 56%).Analytical characterisation: TLC analysis on Merck Silica gel 60F₂₅₄,eluent CH₂Cl₂/hexane 60/40, R_(f): 0.38)

Synthesis of Inventive Resin 2

71.6 g EVAL M100B was dissolved in 280 g dimethyl sulfoxide at 100° C.The mixture was stirred for two hours until complete dissolution. Thereaction temperature was lowered to 80° C. A solution of 1.7 g (17.5mmol) methane sulfonic acid in 30 g dimethyl sulfoxide was added and themixture was stirred for 10 minutes. A solution of 14.2 g (0.07 mol)hexanoic acid (2,2-dimethoxy-ethyl)amide in 42 g dimethyl sulfoxide wasadded and the reaction was allowed to continue for 75 minutes at 80° C.,followed by the addition of a solution of 59.8 g (0.49 mol) salicylicacid in 42 g dimethyl sulfoxide. The reaction was allowed to continuefor 70 minutes at 80° C. A solution of 49 g (0.46 mol) trimethylorthoformate in 21 g dimethyl sulfoxide was added and the reaction wasallowed to continue for 80 minutes at 80° C. The reaction was allowed tocool down to 60° C. and 5.1 g quadrol, dissolved in 14 g dimethylsulfoxide, was added. The reaction mixture was allowed to cool down toroom temperature and diluted with 1700 g 2-methoxy-1-propanol. Themixture was slowly added to 13.5 1 water. The mixture was stirred fortwo and a half hours. Inventive resin 2 was isolated by filtration andwashed with a mixture of 900 ml water and 100 ml 2-methoxy-1-propanol.Inventive resin 2 was treated with a mixture of 4.5 1 water and 0.5 12-methoxy-1-propanol, stirred for 90 minutes, isolated by filtration anddried. 120 g of inventive resin 2 was isolated.

Inventive resin 2 was analyzed using ¹H-NMR spectroscopy. 20 mg of resin2 was dissolved in 0.8 ml DMSO-d6. The aromatic protons of the phenolicmoieties: 7.33 ppm, 7.10 ppm, 6.74 ppm; the phenolic OH: 9.35 ppm; theacetal proton: 5.97 ppm, 5.67 ppm; the methyl protons of the hexanoicgroup: 0.8 ppm; the molar ratio of the aliphatic acetal on the phenolicmoieties: 18 on 100).

Synthesis of Inventive Resin 3 Synthesis ofN-(2,2-dimethoxy-ethyl)benzamide

90.07 g (0.6 mol) benzoic anhydride was dissolved in 500 ml methylenechloride. 63.03 g (0.6 mol) 2,2-dimethoxy-ethylamine, dissolved in 50 mlmethylene chloride, was added dropwise while keeping the temperaturebelow 30° C., followed by the addition of 66.66 g (0.66 mol) triethylamine, dissolved in 200 ml methylene chloride. The reaction was allowedto continue for one hour at room temperature. The reaction mixture wasextracted three times with 250 ml 3 N NaOH, once with 250 ml 1 N HCL andonce with 250 ml satured NaHCO₃. The organic fraction was dried overNa₂SO₄ and evaporated under reduced pressure.N-(2,2-dimethoxy-ethyl)benzamide was purified, using preparativechromatography on a GraceResolv RS80 SiOH 35-45 μm (80 g) column, usinga gradient elution from methylene chloride to methylene chloride/ethylacetate 90/10. 95 g N-(2,2-dimethoxy-ethyl)benzamide was isolated (y:76%). Analytical characterization: TLC analysis on Merck Silica gel60F₂₅₄, eluent CH₂Cl₂/ethyl acetate 80/20, R_(f): 0.3)

Synthesis of Inventive Resin 3

71.6 g EVAL M100B was dissolved in 280 g dimethyl sulfoxide at 100° C.The mixture was stirred for one hour. The reaction temperature waslowered to 80° C. and the polymer was allowed to dissolve over night. Asolution of 1.7 g (17.5 mmol) methane sulfonic acid in 30 g dimethylsulfoxide was added and the mixture was stirred for 10 minutes. Asolution of 14.6 g (0.07 mol) N-(2,2-dimethoxy-ethyl)benzamide in 42 gdimethyl sulfoxide was added and the reaction was allowed to continuefor three hours at 80° C., followed by the addition of a solution of59.8 g (0.49 mol) salicylic acid in 42 g dimethyl sulfoxide. Thereaction was allowed to continue for 30 minutes at 80° C. A solution of49 g (0.46 mol) trimethyl orthoformate in 21 g dimethyl sulfoxide wasadded and the reaction was allowed to continue for 90 minutes at 80° C.The reaction was allowed to cool down to 70° C. and 5.1 g quadrol,dissolved in 14 g dimethyl sulfoxide, was added. The reaction mixturewas allowed to cool down to room temperature and diluted with 1500 g2-methoxy-1-propanol. The mixture was slowly added to 12 1 water. Themixture was stirred for six hours. Inventive resin 3 was isolated byfiltration and washed with a mixture of 900 ml water and 100 ml2-methoxy-1-propanol. Inventive resin 3 was treated with a mixture of 51 water and 0.5 1 2-methoxy-1-propanol, stirred for 90 minutes, isolatedby filtration and dried. 110 g of inventive resin 3 was isolated.

Inventive resin 3 was analyzed using ¹H-NMR spectroscopy. 20 mg of resin3 was dissolved in 0.8 ml DMSO-d6. The aromatic protons of the phenolicmoieties: 7.3 ppm, 7.11 ppm, 6.72 ppm; the phenolic OH: 9.33 ppm; theacetal proton: 5.98 ppm, 5.70 ppm; the benzamide protons: 7.82 ppm, 7.45ppm, 8.2 ppm; the amide NH: 8.42 ppm; the molar ratio of the benzamidemoieties on the phenolic moieties: 18 on 100).

Synthesis of Inventive Resin 4 Synthesis ofN-(2,2-dimethoxy-ethyl)-benzenesulfonamide

69.9 g (0.396 mol) benzene sulfochloride was dissolved in 330 mlmethylene chloride. A solution of 41.6 g (0396 mol)2,2-dimethoxy-ethylamine in 33 ml methylene chloride was added over 30minutes, while keeping the temperature below 35° C. The reaction mixturewas cooled to 0° C. and a solution of 44.1 g (0.436 mol) triethyl aminewas added over 30 minutes. The reaction was allowed to continue for 3hours at room temperature. The reaction mixture was extracted twice with165 ml water, once with 165 ml 3 N HCl and twice with 165 ml saturedNaHCO₃. The organic fraction was dried over MgSO₄ and evaporated underreduced pressure. N-(2,2-dimethoxy-ethyl)-benzenesulfonamide wasisolated as a viscous oil which gradually solidified upon storage. 87.4g (90%) of N-(2,2-dimethoxy-ethyl)-benzenesulfonamide was isolated (TLCanalysis on TLC Silica gel 60 F₂₅₄, supplied by Merck: eluent methylenechloride/methanol: 99/1: R_(f): 0.63).

Synthesis of Inventive Resin 4

71.6 g EVAL M100B was dissolved in 280 g dimethyl sulfoxide at 110° C.The mixture was stirred for two hour to dissolve the polymer completely.The reaction mixture was allowed to cool down to 80° C. A solution of1.7 g (17.5 mmol) methane sulfonic acid in 30 g dimethyl sulfoxide wasadded and the mixture was stirred for 10 minutes. A solution of 17.2 g(0.07 mol) N-(2,2-dimethoxy-ethyl)-benzenesulfonamide in 42 g dimethylsulfoxide was added and the reaction was allowed to continue for one anda half hour at 80° C., followed by the addition of a solution of 59.8 g(0.49 mol) salicylic acid in 42 g dimethyl sulfoxide. The reaction wasallowed to continue for one hour at 80° C. A solution of 49 g (0.46 mol)trimethyl orthoformate in 21 g dimethyl sulfoxide was added and thereaction was allowed to continue for 16 hours at 80° C. The reaction wasallowed to cool down to 70° C. and 5.1 g quadrol, dissolved in 14 gdimethyl sulfoxide, was added. The reaction mixture was allowed to cooldown to room temperature and diluted with 1900 g 2-methoxy-1-propanol.The mixture was slowly added to 15 1 water. The mixture was stirred forsix hours. Inventive resin 4 was isolated by filtration and washed witha mixture of 900 ml water and 100 ml 2-methoxy-1-propanol. Inventiveresin 4 was treated with a mixture of 5 1 water and 0.5 12-methoxy-1-propanol, stirred for 90 minutes, isolated by filtration anddried. 136 g of inventive resin 4 was isolated.

Inventive resin 4 was analyzed using ¹H-NMR spectroscopy. 20 mg ofinventive resin 4 was dissolved in 0.8 ml DMSO-d6. The aromatic protonsof the phenolic moieties: 7.34 ppm, 7.12 ppm, 6.77 ppm; the phenolic OH:9.3 ppm; the acetal proton: 5.98 ppm, 5.67 ppm; the benzenesulfonamideprotons: 7.78 ppm, 7.57 ppm; the molar ratio of the benzenesulfonamidemoieties on the phenolic moieties: 18 on 100).

Synthesis of Inventive Resin 5 Synthesis ofN-(2,2-dimethoxy-ethyl)-4-sulfamoyl-benzamide

240 g (1.2 mol) 4-aminosulfonyl-benzoic acid was dissolved in 2.5 1dimethylacetamide. 233.5 g (1.44 mol) N,N″-carbonyldiimidazole was addedportionwise over 15 minutes. The reaction was allowed to continue for 1hour at room temperature. 151.4 g (1.44 mol) 2,2-dimethoxy-ethylaminewas added and the temperature rose to 45° C. The reaction was allowed tocontinue for 2 hours at room temperature. The solvent was evaporatedunder reduced pressure to one third of its volume and the mixture wasadded to 3 1 water. N-(2,2-dimethoxy-ethyl)-4-sulfamoyl-benzamideprecipitated from the medium.N-(2,2-dimethoxy-ethyl)-4-sulfamoyl-benzamide was isolated byfiltration, washed with water and dried. 228 gN-(2,2-dimethoxy-ethyl)-4-sulfamoyl-benzamide was isolated (y: 65.8%,TLC-analysis on TLC Silica gel 60 F₂₅₄, supplied by Merck: eluentmethylene chloride/methanol: 90/10: R_(f): 0.25).

Synthesis of Inventive Resin 5

71.6 g EVAL M100B was dissolved in 280 g dimethyl sulfoxide at 100° C.The mixture was stirred for one hour. The reaction temperature waslowered to 80° C. and the polymer was allowed to dissolve over night. Asolution of 1.7 g (17.5 mmol) methane sulfonic acid in 30 g dimethylsulfoxide was added and the mixture was stirred for 10 minutes. Asolution of 20.2 g (0.07 mol)N-(2,2-dimethoxy-ethyl)-4-sulfamoyl-benzamide in 42 g dimethyl sulfoxidewas added and the reaction was allowed to continue for four and a halfhours at 80° C., followed by the addition of a solution of 59.8 g (0.49mol) salicylic acid in 42 g dimethyl sulfoxide. The reaction was allowedto continue for 30 minutes at 80° C. A solution of 49 g (0.46 mol)trimethyl orthoformate in 21 g dimethyl sulfoxide was added and thereaction was allowed to continue for one hour at 80° C. The reaction wasallowed to cool down to 70° C. and 5.1 g quadrol, dissolved in 14 gdimethyl sulfoxide, was added. The reaction mixture was allowed to cooldown to room temperature and diluted with 2000 g 2-methoxy-1-propanol.The mixture was slowly added to 17 1 water. The mixture was stirred forsix hours. Inventive resin 5 was isolated by filtration and washed witha mixture of 900 ml water and 100 ml 2-methoxy-1-propanol. Inventiveresin 5 was treated with a mixture of 10 1 water and 1 12-methoxy-1-propanol, stirred for 90 minutes, isolated by filtration anddried. 110 g of inventive resin 5 was isolated.

Inventive resin 5 was analyzed using ¹H-NMR spectroscopy. 20 mg ofinventive resin 5 was dissolved in 0.8 ml DMSO-d6. The aromatic protonsof the phenolic moieties: 7.31 ppm, 7.10 ppm, 6.73 ppm; the phenolic OH:9.3 ppm; the acetal proton: 5.98 ppm, 5.71 ppm; the benzenesulfonamideprotons: 7.98 ppm, 7.87 ppm; the molar ratio of the benzenesulfonamidemoieties on the phenolic moieties: 12 on 100).

Synthesis of Inventive Resin 6

71.6 g EVAL M100B was dissolved in 280 g dimethyl sulfoxide at 100° C.The mixture was stirred for three and a half hour to dissolve thepolymer completely. The reaction mixture was allowed to cool down to 80°C. A solution of 1.7 g (17.5 mmol) methane sulfonic acid in 30 gdimethyl sulfoxide was added and the mixture was stirred for 10 minutes.A solution of 18.4 g (0.07 mol) phtalimidoacetaldhyde diethyl acetal in42 g dimethyl sulfoxide was added and the reaction was allowed tocontinue for one and a half hour at 80° C., followed by the addition ofa solution of 59.8 g (0.49 mol) salicylic acid in 42 g dimethylsulfoxide. The reaction was allowed to continue for 45 minutes at 80° C.A solution of 49 g (0.46 mol) trimethyl orthoformate in 21 g dimethylsulfoxide was added and the reaction was allowed to continue for two anda half hours at 80° C. The reaction was allowed to cool down to 70° C.and 5.1 g quadrol, dissolved in 14 g dimethyl sulfoxide, was added. Thereaction mixture was allowed to cool down to room temperature anddiluted with 1900 g 2-methoxy-1-propanol. The mixture was slowly addedto 15 1 water. The mixture was stirred for two and a half hours. Resin 6was isolated by filtration and washed with a mixture of 900 ml water and100 ml 2-methoxy-1-propanol. Inventive resin 6 was treated with amixture of 5 1 water and 0.5 1 2-methoxy-1-propanol, stirred for 90minutes, isolated by filtration and dried. 115 g of inventive resin 6was isolated.

Inventive resin 6 was analyzed using ¹H-NMR spectroscopy. 20 mg ofinventive resin 6 was dissolved in 0.8 ml DMSO-d6. The aromatic protonsof the phenolic moieties: 7.32 ppm, 7.11 ppm, 6.77 ppm; the phenolic OH:9.3 ppm; the acetal proton: 5.99 ppm, 5.71 ppm; the phtalimido protons:8.21 ppm, 7.84 ppm; the molar ratio of the phtalimido moieties on thephenolic moieties: 16 on 100).

Preparation of the Lithographic Support S-01

A 0.3 mm thick aluminium foil was degreased by spraying with an aqueoussolution containing 34 g/l NaOH at 70° C. for 6 seconds and rinsed withdemineralised water for 3.6 seconds. The foil was then electrochemicallygrained during 8 seconds using an alternating current in an aqueoussolution containing 15 g/l HCl, 15 g/l SO₄ ²⁻ ions and 5 g/l Al³⁺ ionsat a temperature of 37° C. and a current density of about 100 A/dm²(charge density of about 800 C/dm²). Afterwards, the aluminium foil wasdesmutted by etching with an aqueous solution containing 6.5 g/l ofsodium hydroxide at 35° C. for 5 seconds and rinsed with demineralisedwater for 4 seconds. The foil was subsequently subjected to anodicoxidation during 10 seconds in an aqueous solution containing 145 g/l ofsulfuric acid at a temperature of 57° C. and an anodic charge of 250C/dm², then washed with demineralised water for 7 seconds and dried at120° C. for 7 seconds.

Subsequently, the obtained support was post-treated by spraying asolution containing 2.2 g/l polyvinylphosphonic acid (PVPA) for 4seconds at 70° C. onto the support, rinsing the treated support withdemineralised water for 3.5 seconds followed by drying at 120° C. for 7seconds.

The support thus obtained was characterized by a surface roughness R_(a)of 0.45-0.50 μm (measured with interferometer NT3300 and had an anodicweight of about 3.0 g/m² (gravimetric analysis).

Printing Plates PP-01 to PP-06.

Preparation of Printing Plate Precursors PPP-01 to PPP-06

The printing plate precursors PPP-01 to PPP-06 were produced by firstapplying onto the grained and anodized aluminium support S-01 thecoating solution CS-01 containing the ingredients as defined in Table 1by means of a semi-automated coating device. The ingredients of Table 1were dissolved in a mixture of solvents: a methyl-ethylketon (MEK),tetrahydrofuran (THF), dowanol PM, mixture of 40/20/40 and the obtainedcoating solution was applied at a wet coating thickness of 26 μm andthen dried at 100° C. for 1 minute. After drying, the sample was exposedto a hot-warehouse treatment for two days, at 55° C. and 25% relativehumidity.

TABLE 1 Ingredients of the coating solution CS-01 Ingredients* mg/m²Resin (1) 919 IR dye (2) 27 Contrast dye (3) 24 Resole Bakelite (4) 50Polyfox PF652NF(5) 5 Tegoglide 410 (6) 2 Total 1027 *= activeingredients in the coating (1) Comparative Resin 1 and Inventive Resins2 to 6, see above; (2) Infrared cyanine dye, commercially available fromFEW CHEMICALS having the following chemical structure:

(3) Solution in 1-methoxy-2-propanol of 1% by weight of Crystal Violet,commercially available from Ciba-Geigy GmbH. (4) 50 wt. % solution in1-methoxy-2-propanol of Bakelite PF9900LB, a resole commerciallyavailable from Hexion Specialty Chemicals AG.; (5) Solution in1-methoxy-2-propanol of 50% by weight of a perfluorosurfactant, having achemical structure as defined below, commercially available from OmnovaSolutions Inc.

wherein the number average degree of polymerization x + y is about 10and the number average degree of polymerization p + q is about 17.8. (6)Solution in 1-methoxy-2-propanol of 1% by weight of a copolymer ofpolysiloxane and poly(alkylene oxide), commercially available from TegoChemie Service GmbH, Germany.

TABLE 2 printing plate precursors PPP-01 to PPP-06 Printing PlatePrecursor Resin* PPP-01 Comparative Resin 1 comparative PPP-02 InventiveResin 2 inventive PPP-03 Inventive Resin 3 inventive PPP-04 InventiveResin 4 inventive PPP-05 Inventive Resin 5 inventive PPP-06 InventiveResin 6 inventive *The Inventive and Comparative Resins are synthesizedand characterized as described above.Exposure

The printing plate precursors were image-wise exposed at a range ofenergy densities with a Creo Trendsetter, a platesetter having a 20 Winfrared laser head (830 nm), operating at 140 rpm and 2400 dpi,commercially available from Eastman Kodak Corp. The image had a 50% dotcoverage and consisted of a 10 μm×10 μm checkerboard pattern.

Development

The exposed precursors were treated with a developing solution DEV-01 bydip-testing (see below). The developing solution used in the dip-test iswater-based (demineralized water) and the formulation is given in Table3 below. The printing plates PP-01 to PP-06 were obtained.

Procedure of the Dip-test

200 ml of a developer in a cylindrical container is placed in anincubator at 25° C. Subsequently, the exposed printing plate precursoris brought into the container including the developer (developertemperature=25° C.) for a pre-defined time (developer dwell time=25seconds) and then thoroughly rinsed with water.

TABLE 3 Composition of DEV-01 Active ingredients in Ingredients DEV-01(1) DEV-01 g/l Sodium hydroxide (2) 2.3 Sodium metasilicate pentahydrate(3) 66 LiCl 4 Akypo RLM 45CA (4) 3.68 Sodiumsilicate Na₂O + SiO₂ 9.9Briquest 543-25S (5) 1.8 Ralufon DCH (6) 3.7 Preventol Ri50 (7) 1.0Crodateric CYAP (8) 5 SAG220 (9) 0.1 (1) The pH of DEV-01 is 12.9 andthe conductivity 82 mS/cm +/− 0.1 mS/cm (measured at 20° C.). Theingredients are added to demineralized water (total 1 1); (2) 50 wt. %solution of NaOH in water; (3) metasilicate commercially available fromSimaco NV; (4) 90 wt. % alcohol ether carboxylate surfactant solution inwater, commercially available from Kao Chemicals GmbH; (5) 7 g of a 25wt. % solution of the following compound, commercially available fromRhodia Ltd. (Briquest 543-25S):

(6) a 50 wt. % of N,N-dimethyl-N-coco-N-(3-sulfopropyl) ammonium betainein water, from Raschig GmbH.;

(7) 50 wt. % solution in water of Preventol R50, commercially availablefrom Bayer AG.; (8) sodium amphopropionate, commercially available fromLankem Surfactants; (9) SAG220 Anti-Foam Emulsion, polydimethylsiloxaneemulsion in water (20 wt % active material), commercially available fromMomentive Performance Materials Inc..ResultsContrast Evaluation

The contrast between the image and non-image areas was determined afterdevelopment in the developer DEV-01. The contrast is defined as thedifference in optical density between the exposed areas and non-exposedareas after development and is evaluated herein as a visual contrast:

+ indicates a clear contrast between irradiated and non irradiatedareas; and

− indicates no contrast between irradiated and non irradiated areas.

Development was carried out by means of the dip-test as described above.The dilution of the developer solution at which a maximal contrast wasachieved was determined for the different printing plates PP-01 to PP-6.

Results of the Contrast Evaluation

The results of the contrast evaluation are summarized in Table 4 below.The developer was diluted by using demineralized water.

TABLE 4 result of the contrast evaluation Printing Concentration ofDEV-01 Plate 10% 30% 40% 60% 100% PP-01, — — — — + comparative PP-02, —— + + + inventive PP-03, — + + + + inventive PP-04, + + + + + inventivePP-05, — — + + + inventive PP-06, — — + + + inventive

The results show that the printing plates including the Inventive resins2 to 6 show an optimal contrast in a highly diluted developer indicatingan improved solubility of the coating including the inventive resinsaccording to the present invention in the developer solution. PP-03 andPP-04 including respectively inventive resin 3 and inventive resin 4even show a contrast at a 30% (inventive resin 3) and a 10% (inventiveresin 4) diluted developer solution.

Chemical Resistance Evaluation

The solvent or chemical resistance was evaluated as follows:

The printing plate precursors were treated with a droplet (50 μl) of achemical (see Tables 5, 6, 7 and 8 below) for 1 minute at roomtemperature. Subsequently, the droplet was removed with a cotton pad.

The degree of damage the chemical has induced to the coating is visuallyevaluated and scored with a value ranging between 0 and 5:

0=indicates no coating damage;

1=indicates minor coating damage;

2=indicates some coating damage;

3=indicates a lot of coating damage;

4=indicates severe coating damage;

5=indicates complete dissolution of the coating.

The obtained values for each different chemical are added and the sumgives an indication of the chemical resistance: the higher the numberthe lower the chemical resistance of the printing plate.

TABLE 5 fountain solutions Commercially Fountain solutions availablefrom 3520 Emerald Premium Anchor Prisco 3551 + 2 Prisco Europe BvbaPrisco 3551 + 2 (50% Prisco Europe Bvba w/w) Varn Fount 2000 VarnProducts Prisco Webfount 225^(E) Prisco Europe Bvba Prisco Webfount230^(E) Prisco Europe Bvba Antura FS707 web Agfa Graphics NV IsopropanolAcros or Aldrich Prisco 2351 Prisco Europe Bvba

TABLE 6 wash solutions Commercially Wash solutions available fromMethoxypropanol Acros or Aldrich Solco Solstar 4065 Solco OffsetProductsE NV Wash 228 Anchor Antura Wash UV74A Agfa Graphics NV UV Wash CBRAmpla Polygrafia silverwash UV LO (25% w/w)

TABLE 7 plate cleaners Commercially Plate cleaners available fromNormakleen RC910 Agfa Graphics NV Forta Kleen Ultra Agfa Graphics NV LPCPlate cleaner Tower Products

TABLE 8 plate correctors Commercially Plate cleaners available fromReviva Plate Agfa Graphics NV Reviva Plate Pen Agfa Graphics NVResults of the Chemical Resistance Evaluation

The results in Table 9 below show that, compared to the ComparativePrinting Plate PP-01, the chemical resistance of the printing platesincluding a resin according to the present invention, i.e. PP-02 toPP-06, is significantly improved indicating that the resins according tothe present invention significantly enhance the chemical resistance ofthe coating.

TABLE 9 Chemical resistance of the printing plates Chemical Printingplates resistance PP-01 49 comparative PP-02 41 inventive PP-03 45inventive PP-04 42 inventive PP-05 41 inventive PP-08 43 comparative

The invention claimed is:
 1. A copolymer comprising: (i) a plurality ofethylenic moieties A having a structure according to the formula:

wherein R² and R³ independently represent hydrogen; (ii) a plurality ofacetal moieties B having a structure according to the formula:

wherein L¹ is a divalent linking group; X=0 or 1; and R¹ represents anoptionally substituted aromatic or heteroaromatic group including atleast one hydroxyl group; and (iii) a plurality of acetal moieties Cand/or a plurality of acetal moieties D which are different from theplurality of acetal moieties B, and which include at least one nitrogenatom.
 2. The copolymer according to claim 1, wherein the plurality ofacetal moieties C and/or the plurality of acetal moieties D have astructure according to the formulae:

wherein L² and L³ independently represent a linking group; y and zindependently represent 0 or 1; R⁴ and R⁵ independently represent anoptionally substituted alkyl group, or an optionally substitutedaromatic or heteroaromatic group; in the plurality of acetal moieties C,at least one of R⁴ or L² includes a nitrogen atom; and in the pluralityof acetal moieties D, at least one of R⁵ or L³ includes a nitrogen atom.3. The copolymer according to claim 2, wherein the plurality of acetalmoieties C and/or the plurality of acetal moieties D includes theplurality of acetal moieties C.
 4. The copolymer according to claim 3,wherein the plurality of acetal moieties C are present in an amount of 3to 40 mol %.
 5. The copolymer according to claim 1, further comprisingone or more optionally substituted vinyl alcohol moieties E and/or oneor more optionally substituted vinyl moieties F represented by theformula:

wherein R⁶ represents hydrogen, an optionally substituted alkyl group,or an optionally substituted aromatic group or heteroaromatic group. 6.The copolymer according to claim 5, which is represented by thefollowing formula:

wherein L² represents a linking group; R¹ represents an optionallysubstituted aromatic or heteroaromatic group including at least onehydroxyl group; R⁴ represents an optionally substituted alkyl group, oran optionally substituted aromatic or heteroaromatic group; R⁶ is anoptionally substituted alkyl group; m is in a range of 10 to 55 mol %; nis in a range of 15 to 60 mol %; o is in a range of 10 to 60 mol %; p isin a range of 0 to 10 mol %; q is in a range of 3 to 40 mol %; and yrepresents 0 or
 1. 7. A positive-working lithographic printing plateprecursor comprising: a support including a hydrophilic surface or whichis provided with a hydrophilic layer; and a heat- and/or light-sensitivecoating provided thereon; wherein the coating includes the copolymeraccording to claim
 1. 8. The precursor according to claim 7, wherein thecoating includes: a first layer including a binder including asulfonamide group, an imide group, a nitrile group, a urea group, acarboxyl group, a sulfonic acid group, and/or a phosphoric acid group;and a second layer, located above the first layer, including thecopolymer.
 9. The precursor according to claim 7, wherein the coatingincludes: a first layer including a binder including a sulfonamidegroup, an imide group, a nitrile group, a urea group, a carboxyl group,a sulfonic acid group, and/or a phosphoric acid group, and thecopolymer; and a second layer, located above the first layer, includinga phenolic resin selected from a novolac resin, a resol resin, or apolyvinylphenolic resin.